Color pigmented inks used in ink jet printing usually suffer from poor paper fiber show through properties when printed on plain paper. Paper fiber show through is a print quality defect arising because of incomplete wetting of the paper fibers when pigmented inks are laid down resulting in visible white spots on solid areas of the printed image.
To overcome the paper fiber show through problem the ink has to be formulated in such a way that the residence time of ink flow along the surface of the paper is higher, so that when the fluidity of pigment particles vanish due to the loss of the ink vehicle (mainly water and humectants) the pigment particles settle down on the top surface of the plain paper thus increasing the probability to stain the fibers on the surface of the paper and reducing paper fiber show through. The two main methods used to reduce fiber show through are 1). Increasing the viscosity of the ink by increasing the humectant loading to reduce penetration. 2) Reducing the surface tension thus in turn wetting all the fibers by enhancing the spreading rate. In the latter case the mobility of ink is reduced by the spreading rate. The ink spreading causes the ink film thickness to reduce drastically thus effecting reduced mobility and uniform staining of the paper fiber.
The drawbacks of adding higher amounts of high boiling humectants to increase viscosity are the slow drying rate of ink thus worsening the smear properties of ink on paper and poor jetting characteristics.
The drawbacks of reducing surface tension with pigmented ink are poor ink stability (shelf life) and poor jetting due to increased puddling of ink during jetting.